AMD's Bulldozer and Bobcat: New Twists in CPU Core Design

AMD today announced details of two new CPU cores that will provide the backbone of its chip designs for the next few years. "Bulldozer" is designed for the company's upcoming server and desktop chips; while "Bobcat" will power AMD's first "accelerated processing unit (APU)", aimed at notebook and netbook markets. While the designs follow the basic progression we've been expecting, both have some interesting twists .

AMD today announced the details of two new CPU cores that will provide the backbone of its chip designs for the next few years. "Bulldozer" is designed for the company's upcoming server and desktop chips; while "Bobcat" will power AMD's first "accelerated processing unit (APU)," which is aimed at notebook and netbook markets. While the designs follow the basic progression we've been expecting, both have some interesting twists .

It's rare that a CPU company would announce two cores at the same time, but Chekib Akrout, Senior VP and General Manager for Technology Development, Said it was important because of the various different goals and requirements of the market; with Bulldozer being aimed at the high-end (where performance is most important within a power envelope) and Bobcat at the low-end (where energy-efficency is most important). There may be a little overlap -- you might see a low-voltage part with Bulldozer cores -- but in general, these are pretty distinct markets.

More after the jump.

Bulldozer

In a number of ways, I thought Bulldozer was most surprising. Since higher-clock speeds in processors are pretty much out (because it would generate too much heat), most of the high-end chips we've seen for the past few years have focused on adding more cores. Core multiprocessing (CMP) certainly works, but it uses a lot of area on the die. Symmetric multithreading (SMT), or in Intel's parlance, HyperThreading, does add performance, but only when the individual cores are not being completely used. Akrout says it might improve typical performance by 30 percent.

With Bulldozer, AMD is taking an approach that is somewhere in the middle. In this design, each module has two full integer processing units, but shares a floating point scheduler with two 128-bit floating point multiply accumulate (FMAC) units. In addition to the floating point unit, each set of two integer cores will share fetch and decode components, as well as a single Level 2 cache. This way for integer operations, it acts as two full cores, but shares a lot of pieces, thus reducing the die size (which tremendously impacts the cost of manufacturing) and power consumption. It's quite an interesting trade off.

Bulldozer also has support for new x86 instructions, including those for SSE (streaming SIMD extension) 4.1 and 4.2 ; AVX (Advanced Vector Extensions); and XOP. Basically, these are new commands used for multimedia and for floating-point intensive calculations. Akrout said the chip should offer faster single-thread performance as well, thanks to a state-of-the art microarchitecture, which optimizes execution units and branch prediction.

Multiple Bulldozer cores will be combined to create the actual chips AMD is planning. First up, should be the 8-core "Valencia" server chip (and the dual-die 16-core version called "Interlagos), and an 8-core desktop version code-named "Zambezi."

These are being produced on Globalfoundries' 32nm high-k/metal gate process (the company's first high-k/metal gate chips); and are expected to be out sometime in 2011.

AMD wouldn't be more specific on dates, clock speeds, or prices, and we won't really know performance until the chip is released, of course. But the company said it should provide 33 percent more cores and 50 percent more throughout than the existing "Magny-Cours" design. While the die size is "somewhat bigger," it is designed to fit in the same sockets as the current Magny-Cours design (sold under the Operton name) and to be a drop-in replacement.

Bobcat

Bobcat takes a very different approach: it's a more traditional core design, with a strong emphasis on low-power performance. AMD says it has designed the cores for power-optimized execution, with a micro-architecture that minimizes data movement and unnecessary reads, along with power-gating and low-power states. The company claims these cores are capable of running with under 1 watt of power. This core features "out of order execution" -- something common in high-end processors these days, but not featured in Intel's Atom chip. AMD estimates it will have 90 percent of the performance of today's mainstream notebook parts (say, the Athlon II chip), while using less than half of the silicon area and using "a fraction of the power."

What really sets it apart, of course, is that it is planned to be used in a "Fusion" chip -- one that combines traditional CPU and GPU functions in the same chip. In this case, AMD is planning on combinined two Bobcat cores, along with a graphics engine (a "single instruction multiple data" engine) and a unified video decoder and the traditional platform interfaces for memory and the bus, into a single chip die, codenamed "Ontario."

AMD recently changed its roadmap so that this chip, which will be manufactured on TSMC's 40nm process, should be appearing in early 2011. Ontario is designed for notebook computers and the "netbook" segment, where it should let AMD compete against Intel's Atom chip.

Both Bobcat and Bulldozer are interesting designs, and it's interesting how chip design has changed from the era where ever-faster clock speeds drove performance enhancements. Going forward, Akrout says he sees the big issue as packing more functionality and performance into a limited power envelope, and dealing with fixed resources in terms of area and clock frequency in the most optional way for different kinds of applications.

Over the next five to ten years, he sees more smaller engines to respond to specific needs (such as encryption), simplified instruction sets, and changes in the memory subsystem away from the traditional combination of level 1, 2, and 3 caches.

Of course, other vendors are working on new cores and new chips as well. I expect to hear more about Intel's SandyBridge at its Developer Forum next month. And in all these cases, we won't really know how well they work until we get actual systems built around the designs. But Bulldozer and Bobcat -- and the processors built around them -- look like big steps forward for AMD.

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